India has reported cases of the Zika virus, the World Health Organization said, adding that efforts should be made to strengthen surveillance.

The WHO said that on May 15 India's health ministry reported three confirmed cases from the western state of Gujarat. Cases were detected during testing in February and November last year, while one was detected in January this year, according to the statement, which was released on Friday but did not gain public attention until Saturday.

An Indian federal health ministry official said states were following standard protocols and there was "nothing to worry" about. The ministry had in March cited one confirmed case of Zika - from January of this year in Gujarat - while answering a question in India's parliament.

"These findings suggest low-level transmission of Zika virus and new cases may occur in the future," the WHO said in the statement on its website.

"Zika virus is known to be circulating in South-East Asia Region and these findings do not change the global risk assessment."

In its most recent outbreak, Zika, which is mainly a mosquito-borne disease, was identified in Brazil in 2015 and has been spreading globally.

When the virus infects a pregnant woman, it can cause a variety of birth defects including microcephaly, where the baby's head is abnormally small.